A Magnetic Tunnel Junction (MTJ) includes two ferromagnets (FMs) separated by a thin insulator. If the insulating layer is thin enough, electrons can tunnel from one FM into the other. Each of the FMs has a direction of magnetization. When the directions of magnetization are aligned, or parallel, then the electrons flow more freely across the barrier from one FM to the other. When the directions of magnetization are oppositely aligned, or antiparallel, then the electron flow is more restricted. The direction of the two magnetizations can be switched by an external magnetic field. Using this phenomenon, an MTJ can be switched between two states of tunneling resistance, one with relatively low resistance and one with relatively high resistance.
Typically, the magnetization of one of the ferromagnetic layers is held fixed by forming a layer of antiferromagnetic material next to that FM. This is sometimes referred to as “pinning” the FM. Additionally, an external magnetic field can be generated by an electrical current flowing through a conductor. This requires a significant amount of power and creates waste heat.
Complementary Metal-Oxide Semiconductor (CMOS) based technologies have been made increasingly smaller. As continued miniaturization may be difficult, various “beyond-CMOS” technologies are being considered. Magneto-electrics (MEs) are rapidly emerging as a key technology for applications in various beyond-CMOS spin-based device technologies. An ME can create a magnetic field using an applied voltage instead of a flowing electrical current. An ME MTJ is a device based on MEs that shows great promise for future memory and logic applications. In an ME MTJ, switching is achieved by reversing the magnetization of the so-called “free” FM of an MTJ. Specifically, the magnetization reversal is induced by means of the voltage-control of magnetism of a proximal ME layer. Voltage control minimizes power consumption by making use of exchange biasing between the antiferromagnetic (AFM) ME layer and the free FM. This makes the ME MTJ an extremely low power device which can typically operate with a supply of +/−0.1-0.2 V. Boundary magnetization at the ME layer interface has the inherent property of non-volatility. This makes ME MTJ attractive for memory applications and perhaps logic applications. So far, the use of an ME MTJ for logic applications has been limited.
Accordingly, logic applications for ME MTJs are needed for reducing energy consumption and providing non-volatility.